There is growing evidence to indicate an interaction between the biologically active constituent of marijuana, delta-9-tetrahydrocannabinol (THC), and testosterone (T) in the central nervous system. However, little information is currently available regarding the functional consequences of this interaction on behavior. The proposed study will test the following hypotheses: 1)T replacement will attenuate the disruptive effects of systemically administered THC on overall response rate and percent errors in castrated male rats responding under a multiple schedule of repeated acquisition and performance of behavioral chains, 2) T replacement will differentially affect levels and function of cannabinoid receptor binding, as measured by quantitative receptor autoradiography, in brain areas implicated in learning and memory and will potentiate decreases in cannabinoid receptor binding induced by chronic administration of THC, 3) T replacement will attenuate the disruptive effects of intrahippocampally-administered THC on overall response rate and percent errors in ovariectomized rats responding under a multiple schedule. These results will provide, for the first time, information regarding the interactive effects of testosterone and THC on cognitive behavior.